Recent Developments of Medium-Range EPS at JMA
Haruki YAMAGUCHI*, Masakazu HIGAKI, and Masayuki KYOUDANumerical Prediction Division, Japan Meteorological Agency, Tokyo,
Japan
1The 4th THORPEX-Asia Science Workshop (31 October 2012)
Outline• Introduction of One-week EPS and Typhoon
EPS of JMA • Experiment A
– Impact of enhancing horizontal resolution of forecast model in One-week EPS
• Experiment B– Impact of increasing ensemble size in typhoon
track forecasts in Typhoon EPS
• Summary
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Specification of medium-range EPS at JMA
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More detailed information is available at the JMA part of the latest “WMO Technical Progress Report on GDPFS and NWP Research” and the standardized EPS documentation in Excel spreadsheet format at http://tigge.ecmwf.int/models.html
The 4th THORPEX-Asia Science Workshop (31 October 2012)
Will be extended to 264 hours by next March
Planned upgrades of the two EPSs• Both EPSs: Enhancing forecast model
– Apply several improvements in high-res deterministic forecast GSM, including increase of vertical levels
– Increase horizontal resolution for better weather forecast in Japan
• One-week EPS: Increasing frequency of operation to two times in a day as almost retaining ensemble size per day to offer forecasters more fresh materials.
• Typhoon EPS: Almost doubling ensemble size to improve reliability of probabilistic typhoon track forecasts
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Operation Planned upgrades
One-week EPS Typhoon EPS One- week EPS
Typhoon EPS
Horizontal resolution
TL319 (~55km) TL479 (~40km)
Vertical levels 60 levels up to 0.1hPa 100 levels up to 0.01hPa
Initial time 12UTC 00,06,12,18UTC 00,12UTC Not changed
Ensemble size 51 11 27 25
Experiments• Planned changes are broken down into several small
changes and have been examined by multiple experiments. Two of them are introduced.
• Experiment A : Enhancing horizontal resolution of One-week EPS to examine impacts in– Reducing “gap” with high-res deterministic GSM– Better orographic effects
• Experiment B: Increasing ensemble size of Typhoon EPS to examine impacts in– Improving probabilistic typhoon track forecasts
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Experiment A: Impact of enhancing Horizontal resolution
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One-week EPS Operation Experiment A
Horizontal resolution TL319 (~55km) TL479 (~40km)
Ensemble size 51 (27 when comparing to experiment)
27
Initial time 12 UTC 12 UTC (00 UTC omitted)
TL319 TL479
Equivalent horizontal grid representing land around Japan
Better resolve Japan archipelago
Tropical cyclone• Typhoons reproduced in the experiment tend to get closer to those of
high-res GSM in the ways that:– The typhoons have deep center with strong wind near the center– Actually they are often too strong compared to analysis
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Unperturbed member of the EPSs, initial time 27 AUG 2011 12UTC, FT 72 hr
Operation (TL319) Experiment (TL479) GSM (JMA’s high-res TL959 forecast)
Sur
face
win
d sp
eed
[m/s
]
west-east section across the typhoon centerSea level pressure [hPa] Surface
wind speed [m/s]
TL959TL479TL319 TL959
TL479TL319deep
strong
Analysis (For this case, forecasts are too strong)
Winter monsoon• Typical weather with winter monsoon
– Upwind orographic precipitation and stripe precipitation pattern in Pacific
• Experiments shows finer precipitation pattern• Not so obvious difference of upwind orographic precipitation
between operation and experiment
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Unperturbed member of the EPSs, initial time 23 DEC 2011 12UTC, FT 72 hr
Operation (TL319) Experiment (TL479) GSM (JMA’s high-res TL959 forecast)
Observation (For this case, forecasts are too weak)
Pre
cipi
tatio
n [
mm
/24h
r]
Impact in precipitation probability
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Operation (TL319)
Experiment (TL479)
Initial time 2012/1/7 12UTC, FT144
Probability of precipitation exceeding 1mm/24hr
DIFF(Experiment-Operation) & Observation
[%]
[%]
[%]
Green dot (event occurred)Black dot (not)
In some cases, there is a difference near border of orographic precipitation
Verification of precipitation probability• AMeDAS rain gauge observation on land across Japan, converted
0.5625deg x 0.5625deg verification grid, is compared with forecast• Period: 2012 JAN 3 ~ FEB 3 12UTC• Brier score of probability of precipitation exceeding 1mm/24hr
– Brier skill score is improved by improving both reliability and resolution term.– Score of Experiment is also comparable or superior to that of 51-member Operation
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0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 24 48 72 96 120 144 168 192 216
Brie
r ski
ll sc
ore
Forecast time [hr]
Operation(M27) Operation(M51) Experiment(M27)
0.020.0220.0240.0260.028
0.030.0320.0340.0360.038
0.04
0 24 48 72 96 120 144 168 192 216
Brie
r sco
re r
elia
blit
y te
rm
Forecast time [hr]
Operation(M27) Operation(M51) Experiment(M27)
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0 24 48 72 96 120 144 168 192 216
Brie
r sco
re r
esol
ution
ter
m
Forecast time [hr]
Operation(M27) Operation(M51) Experiment(M27)
Reliability term of Brier score
Resolution term of Brier score
Brier skill score
Experiment B: Increasing ensemble size of Typhoon EPS
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Typhoon EPS Operation Experiment B
Horizontal resolution TL319 (~55km) Not changed
Ensemble size 11 25
Initial time 00,06,12,18 UTC Not changed
Typhoon EPS has the following features:• Identical forecast model with One-week EPS• Specialized for Typhoon forecast in RSMC Tokyo• Initial perturbations are composed of singular vectors targeted at RSMC Tokyo and around typhoons like the right figure• High frequency operation (up to 4 per day) but with smaller ensemble size than One-week EPS Targeted areas around up to three typhoons
Targeted area over RSMC Tokyo
Impact on increase of ensemble size
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Operational EPS (11 members) Experiment (25 members)
Ensemble TC tracks of Typhoon “Talas” up to 120 hours derived from the Typhoon EPS (left panel) and an experimental EPS (right panel). - Initial time is 12UTC 28th August 2011. - Black lines and color lines indicate the best track and the forecast tracks, respectively.
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Verification of strike probability
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Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC
Reliability term is improved
13The 4th THORPEX-Asia Science Workshop (31 October 2012)
Reliability diagrams of strike probability that the center of a typhoon will pass within 120km during the next five days
Operation(11 members)
Experiment(25 members)
Close look to position error of track forecasts
• There found no significant improvement of ensemble mean track forecasts between operation and experiment.
• Common difficulties in the both cases are found:– Too large ensemble spread during earlier forecast time, possibly be deteriorating ensemble mean– Spread seems not to be enough for large error cases during later forecast time
1414The 4th THORPEX-Asia Science Workshop (31 October 2012)
Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC
Position error of ensemble mean forecast is larger than that of control run.
Need to tune amplitude of initial perturbations.
For large position error cases, larger spread is desired.
Summary• JMA prepares the next upgrade of its two EPSs. Two
preliminary experiments are introduced.• Results of the experiment enhancing horizontal resolution of
One-week EPS– Expected tendency of resemblance to high-res GSM– The center of typhoons tend to be stronger though they often exceed
analysis– Improvement of precipitation probability forecast in winter
• Results of the experiment increasing ensemble size of Typhoon EPS– Improvement of reliability of strike probability– Little impact in ensemble mean track forecast.– Regardless of ensemble size, there is a need to tune ensemble spread
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